<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <form action="">
        <div>
            <input type="text">
        </div>
        <div>
            <input type="text">
        </div>
        <div>
            <input type="text">
        </div>
        <div class="btn">
            <div class="btnInner"></div>
        </div>
        <style>
            .btnInner {
                background: green;
                height: 100%;
                border-radius: 50px;
                z-index: 1;
                position: relative;
            }
            .btn {
                color: red;
                width: 200px;
                height: 50px;
                z-index: 1;
                position: relative;
            }

            .btn::before {
                display: block;
                content: " ";
                position: absolute;
                left: -2px;
                height: 50px;
                width: 50px;
                border-radius: 50%;
                background-image: linear-gradient(0deg,black,black 20%,transparent 0,transparent);
                box-sizing: border-box;
                z-index: 0;
            }

            .btn::after {
                display: block;
                content: " ";
                position: absolute;
                right: -2px;
                border: 2px solid green;
                height: 50px;
                width: 50px;
                border-radius: 50%;
                top: -2px;
            }
        </style>
    </form>
</body>

</html>